1. Field of the Invention
The present invention pertains to metallized polymer mirror constructions having improved durability, and represents an improvement over conventional polymer mirror constructions by virtue of having an oxide layer interposed between an outer layer of polymeric material and the reflective layer of silver. The oxide acts as an adhesive layer and impedes the initiation of delamination as well as the propagation of delamination (tunneling), if initiation of delamination occurs. The interposed oxide layer further provides protection to the silver layer and slows corrosion of the silver layer. In a preferred construction, a copper layer is disposed between the layer of silver and the adhesive layer, and in this preferred construction, the copper also helps slow corrosion of the silver.
2. Description of the Prior Art
Current polymer mirror designs use a vacuum metallized polymer that is attached by an adhesive layer to a substrate; however, in harsh, outdoor environments, these current polymer mirror designs tend to degrade by delamination and by silver corrosion. In particular, it has been noted in these prior art designs with conventional constructions that the adhesion between the polymer (i.e., polymethylmethacrylate) and silver is weak and deteriorates in the presence of moisture. Further, the polymer can delaminate from the silver and degrade specular reflectance.
Therefore, a need exist in the polymer mirror design art to identify metallized polymer constructions that can be used in commercial mirror systems in place of materials currently being used, to provide sufficient durability. In identifying metallized polymer constructions capable of alleviating or lessening insufficient durability, there is a need to address the primary problem that current metallized polymer mirrors do not maintain specular reflectance in a harsh, outdoor environment, and that current materials degrade by delamination and by silver corrosion--and that the successful resolution to these problems would slow both types of degradation.
In essence, the identification of metallized polymer constructions capable of resolving the foregoing problems would reside in selecting the proper choice and placement of materials, so that the factors that contribute to the degradation of the reflective surface are controlled and isolated from that surface.
U.S. Pat. No. 1,998,088 discloses a metal backed light reflector comprising, a glass reflector body, a reflective film of silver on the body, a metal backing layer metallically united to the film, and material on the backing comprising on the exterior a transparent varnish, and beneath the varnish a visible metallic powder. In other words, this patent pertains to metal back layers as used with glass mirrors.
There is disclosed in U.S. Pat. No. 4,944,581, a reflection mirror of a multi-layer film for a synthetic resin substrate, wherein the polymer, polymethylmethacrylate is the substrate and wherein silver is backed with copper. In particular, a thick prism substrate of polymethylmethacrylate is used to obtain a rigid structure for use in instruments. There is no indication of use of a very thin polymethylmethacrylate polymer film to obtain a thin, flexible, large-area mirror that can conform to curved substrate needs for solar applications; instead, the mirrors used in this patent are rear face reflection mirrors.
U.S. Pat. No. 4,457,587 disclose a reflector having a base which may be a metallic material of an alloy of aluminum with copper, a smoothing layer, an aluminum reflecting layer, and a light-transmitting water-insoluble inorganic oxide layer; however, the gist of this patent is its reference to mirrors of aluminized metal substrates with no reference to copper back layers.
A laminated reflective panel comprising a mirror sheet of glass, a reflective coating of silver, and a protective layer of copper is disclosed in U.S. Pat. No. 4,511,618; however, the reference in this patent is to glass mirrors.
U.S. Pat. No. 4,550,986 discloses a layered mirror comprising an acrylic sheet, and a reflecting layer of silvering or coppering bonded by an adhesive to a foam layer which relieves the thick acrylic that constitutes a rigid structure.
U.S. Pat. No. 2,103,538 discloses a reflector of a concavo convex configuration in which glass is polished on both surfaces; wherein a layer of silver is deposited on the convex surface and a layer of copper is superimposed on the silver; however, it is to be noted that the reference in this patent is to copper back layers applied to glass mirrors, and this is common place. There is no reference to the characteristics of copper as used with polymeric mirrors.